Ceramics heat exchanger and production method thereof

ABSTRACT

In a heat exchange element  1 , first fluid circulation portions  5  having a honeycomb structure having a plurality of cells separated by ceramic partition walls  4 , extending through in an axial direction from one end face  2  to the other end face  2 , and allowing a heated medium as a first fluid to flow therethrough and second fluid circulation portions  6  being separated by ceramic partition walls  4 , extending in the direction perpendicular to the axial direction, allowing a second fluid to flow therethrough, transferring heat to a medium to be heated as the second fluid are alternately formed as a unit. The cells  3  on the first fluid circulation portion  5  side are smaller than the cells  3  on the second fluid circulation portion  6  side, and the partition walls have a density of 0.5 to 5 g/cm 3  and a thermal conductivity of 10 to 300 W/mK.

FIELD OF THE INVENTION

The present invention relates to a ceramics heat exchanger fortransferring heat of the first fluid (high temperature side) to thesecond fluid (low temperature side).

BACKGROUND OF THE INVENTION

Generally, driving energy of an automobile is merely about 25% of fuelcombustion energy. The rest becomes an energy loss such as a coolingloss (engine cooling water of 30%), an exhaust gas loss (exhaust gas of30%), and the like. After 2010, in the automobile field, CO₂ reductionhas been becoming strict, and fuel efficiency requirements have beenbeing tightened. Therefore, many automobile companies work on reductionof the exhaust gas loss, for example, exhaust heat recovery technologyas a measure for reducing the energy loss to improve automobile gasmileage.

Patent Document 1 discloses a ceramic heat exchange element where flowpassages for a heated medium are disposed from one end face to the otherend face of a ceramic main body and where flow passages for a medium tobe heated are formed in a direction perpendicular to the flow passagesfor the heated medium between the flow passages for the heated medium.

Patent Document 2 discloses a ceramic heat exchanger where a pluralityof ceramic heat exchange elements each having flow passages for a heatedfluid and flow passages for a fluid to be heated formed therein aredisposed in a casing with interposing a cord-shaped sealing materialmade of unfired ceramic between bonding faces of heat exchange elements.

The Patent Document 3 discloses an exhaust system heat exchanger capableof inhibiting a cooling medium in an external cylinder from having hightemperature. In addition, the Patent Document 4 discloses an exhaust gasheat recovery unit capable of relaxing thermal stress with a simplestructure. Further, Patent Document 5 discloses an exhaust gas heatexchanger which is miniaturized and which can suppress costs with astructure capable of easy installation.

[Prior Art Document] [Patent Document]

[Patent Document 1] JP-A-61-24997

[Patent Document 2] JP-B-63-60319

[Patent Document 3] JP-A-2007-285260

[Patent Document 4] JP-A-2007-332857

[Patent Document 5] JP-A-2006-284165

Each of the Patent Documents 1 and 2 shows a structure where a heatedfluid flows thereinto from the flow passages having a slit structure andwhere a medium to be heated flows thereinto from honeycomb structuredflow passages to reduce the influence of a pressure loss of the heatedfluid. However, the structure does not have good efficiency regardingthe heat exchange.

The Patent Document 3 shows a structure where a heat exchange passagefor water cooling is disposed in the periphery of a heat exchangepassage for exhaust gas, it is more difficult to exchange heat in thecentral portion of the exhaust gas flow passages, and the heat exchangerate is low as a whole. In addition, in the Patent Document 4, thestructure is constituted of an evaporation portion (first heat exchangeportion), a heat-transfer fin, and a condensation portion (second heatexchange portion) However, since it exchanges heat by means of aheat-transfer fin without directly exchanging heat, the heat exchangeefficiency is low. On the other hand, in the Patent Document 5, a heatexchange core portion obtained by laminating a plurality of flat platesare formed in the route where exhaust gas passes, and a cooling liquidflow passage extending through in the thickness direction is formed.However, since exhaust gas flows through a gap between the flat plates,though the heat exchanger has high heat exchange efficiency incomparison with those of the Patent Documents 3 and 4, the contact areais not always large for heat transfer from the exhaust gas to the flatplates, and insufficient heat exchange may be caused between the exhaustgas and the cooling liquid.

The present invention aims to provide a heat exchanger having high heatexchange efficiency in comparison with conventional heat exchangeelements, heat exchangers, and the like and realizing miniaturization,weight saving, and cost reduction and a production method thereof.

SUMMARY OF THE INVENTION

The present inventors found out that the aforementioned problems can besolved by a ceramics heat exchanger provided with a heat exchangeelement where the first fluid circulation portions for allowing a heatedmedium as the first fluid to circulate and the second fluid circulationportions for transferring heat to a medium to be heated as the secondfluid are alternately formed as a unit. That is, according to thepresent invention, there are provided the following ceramics heatexchanger and production method thereof.

[1] A ceramics heat exchanger comprising: first fluid circulationportions having a honeycomb structure having a plurality of cellspartitioned by ceramic partition walls, extending through in an axialdirection from one end face to the other end face, and allowing a heatedmedium as a first fluid to flow therethrough, and second fluidcirculation portions being partitioned by ceramic partition walls,extending in the direction perpendicular to the axial direction, beingisolated from the first fluid circulation portions by the partitionwalls to be capable of heat conduction, allowing a second fluid to flowtherethrough, receiving the heat of the first fluid circulating in thefirst fluid circulation portions by means of the partition walls, andhaving cells for transferring heat to a medium to be heated as thesecond fluid; wherein the first fluid circulation portions and thesecond fluid circulation portions are alternately formed as a unit, thecells on the first fluid circulation portion side are smaller than thecells on the second fluid circulation portion side, and the partitionwalls have a density of 0.5 to 5 g/cm³ and a thermal conductivity of 10to 300 W/mK.

[2] The ceramics heat exchanger according to the above [1], wherein eachof the second fluid circulation portions has a slit structure having noseparating partition wall or having 1 to 50 separating partition walls.

[3] The ceramics heat exchanger according to the above [1] or [2],wherein a plurality of the heat exchangers are bonded together by meansof a bonding material layer of heat resistant cement.

[4] The ceramics heat exchanger according to any one of the above [1] to[3], wherein SiC is contained in the ceramics constituting the partitionwalls.

[5] The ceramics heat exchanger according to any one of the above [1] to[4], wherein the ceramics constituting the partition walls isSi-impregnated SiC.

[6] The ceramic heat exchanger according to any one of the above [1] to[5], wherein the first fluid is gas, and the second fluid is liquid.

[7] The ceramic heat exchanger according to any one of the above [1] to[6], wherein a catalyst is loaded on wall surfaces of the first fluidcirculation portions.

[8] A method for manufacturing a ceramics heat exchanger comprising thesteps of: forming a honeycomb structure having a plurality of cellsseparated by ceramic partition walls and extending through in an axialdirection from one end face to the other end face by extruding a ceramicforming raw material, forming slits with regard to a part of a pluralityof cell lines to extend through the partition walls forming the cellsand the outer peripheral wall of the honeycomb structure in thedirection perpendicular to the axial direction, and forming pluggedportions plugged with a plugging member on one end face and the otherend face of the cells in the cell lines where slits are formed.

In a ceramics heat exchanger of the present invention, attention is paidto heat and a heat exchange element which exchanges heat in exhaust heatrecovery technology, and the heat exchanger realizes high heat exchangeefficiency, miniaturization, weight saving, and cost reduction incomparison with a conventional heat exchange element (heat exchanger orits device).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing an embodiment of a heat exchangeelement of the present invention.

FIG. 2A is a view showing an embodiment of an end face in the axialdirection of a heat exchange element of the present invention.

FIG. 2B is a view showing another embodiment of an end face in the axialdirection of a heat exchange element of the present invention.

FIG. 3A is a view showing an embodiment viewed from the outer peripheralwall side where slits are formed.

FIG. 3B is a view showing another embodiment viewed from the outerperipheral wall side where slits are formed.

FIG. 4 is a view showing an embodiment where a plurality of heatexchange elements are bonded together.

FIG. 5 is a view showing an embodiment of a ceramics heat exchanger ofthe present invention where a heat exchange element is disposed therein.

FIG. 6 is a view showing an embodiment of a heat exchange element wheresome of the partition walls have different thickness.

FIG. 7A is a view from the inlet side of the first fluid, showing anembodiment where an end face in the axial direction of partition wallsof a heat exchange element is a tapered face.

FIG. 7B is a cross-sectional view taken along a face in parallel withthe axial direction, showing an embodiment where an end face in theaxial direction of partition walls of a heat exchange element is atapered face.

FIG. 8A is a view showing an embodiment of a heat exchange element wherecells having different sizes are formed.

FIG. 8B is a decomposition perspective view of the embodiment of FIG.8A.

FIG. 8C is a decomposition perspective view showing an embodiment of acircular columnar heat exchange element where cells having differentsizes are formed.

FIG. 8D is a view showing an embodiment of a heat exchange element wherethe size of the cells is changed.

FIG. 8E is a view showing an embodiment of heat exchange element wherethe thickness of the partition walls is changed.

FIG. 9A is a view showing an embodiment of a heat exchange element wherethe thickness of the partition walls is increased from the inlet side ofthe first fluid toward the outlet side.

FIG. 9B is a view showing an embodiment of a heat exchange element 1where the first fluid circulation portion is gradually narrowed from theinlet side toward the outlet side of the first fluid.

FIG. 10A is a view showing an embodiment where the cells of a heatexchange element has a hexagonal shape.

FIG. 10B is a view showing an embodiment where the cells of a heatexchange element has an octagonal shape.

FIG. 11 is a view showing an embodiment of a heat exchange element whereR portions are formed at the corners of the cells.

FIG. 12A is a view showing an embodiment of a heat exchange elementhaving protruding fins in a cell.

FIG. 12B is a view showing another embodiment of a heat exchange elementhaving fins in a cell.

FIG. 13A is a view showing an embodiment of a heat exchange elementwhere a part of the cell structure is densified.

FIG. 13B is a decomposition perspective view of the embodiment of FIG.13A.

FIG. 13C is a decomposition perspective view showing an embodiment of acircular columnar heat exchange element where cells having differentsizes are formed.

FIG. 13D is a view showing an embodiment of a heat exchange elementwhere the cell density is gradually changed.

FIG. 13E is a view showing an embodiment of a heat exchange elementwhere the cell structure is changed by changing the wall thickness.

FIG. 14A is a view showing an embodiment of a heat exchanger where thedirection of the partition walls is offset between the front part heatexchange element and the rear part heat exchange element.

FIG. 14B is a view showing an embodiment of a heat exchanger where theposition of the partition walls is offset between the front part heatexchange element and the rear part heat exchange element.

FIG. 15 is a view showing an embodiment of a heat exchanger where thecell density of the rear part heat exchange element is higher than thatof the front part heat exchange element.

FIG. 16 is a view showing an embodiment of a heat exchanger having aconstitution where the cell density of the front part heat exchangeelement is high on the inside and low on the outer periphery side andwhere the cell density of the rear part heat exchange element is low onthe inside and high on the outer periphery side.

FIG. 17A is a view showing an embodiment of a heat exchanger where aplurality of heat exchange elements are disposed, each of the heatexchange elements has two semicircular regions having different celldensities, the heat exchange elements are disposed so that the celldensity distribution is different between the front part heat exchangeelement and the rear part exchange element.

FIG. 17B is a decomposition perspective view of the embodiment of FIG.17A.

FIG. 17C is a view showing an embodiment of a heat exchange elementhaving two prismatic columnar regions having different cell densities.

FIG. 18A is a view showing an embodiment of a heat exchanger having aconstitution where the front part heat exchange element is plugged onthe outer periphery side and where the rear part heat exchange elementis plugged on the inside.

FIG. 18B is a view showing an embodiment of a heat exchanger obtained bydisposing heat exchange elements where plugged prismatic column andunplugged prismatic column are combined in the front part position andthe rear part position.

FIG. 19A is a view showing an embodiment of a heat exchange elementwhere the inlet and the outlet of the first fluid circulation portionare alternately plugged.

FIG. 19B is an A-A cross section in FIG. 19A.

FIG. 20 is a cross section of the first fluid circulation portion,showing an embodiment where porous partition walls are formed in thefirst fluid circulation portion.

FIG. 21 is a view showing an embodiment of a heat exchange element wherethe thickness of the partition walls forming the first fluid circulationportion is gradually increased from the center toward the outerperiphery in a cross section perpendicular to the axial direction.

FIG. 22 is a view showing an embodiment of a heat exchange element usinga honeycomb structure where the external shape is an ellipse and wherepartition walls on one side is formed thick.

FIG. 23 is a view showing an embodiment where the outer peripheral wallof a honeycomb structure forming the heat exchange element is thickerthan the partition walls forming the cells.

FIG. 24 is a view showing an embodiment where the external shape of thehoneycomb structure forming the heat exchange element is flattened.

FIG. 25A is a perspective view showing an embodiment where the end faceon the inlet side of the first fluid is inclined.

FIG. 25B is a perspective view showing another embodiment where the endface on the inlet side of the first fluid is inclined.

FIG. 25C is a perspective view showing still another embodiment wherethe end face on the inlet side of the first fluid is inclined.

FIG. 26 is a view showing an embodiment where the end face on the inletside of the first fluid of the honeycomb structure forming a heatexchange element is formed to have a depressed face shape.

FIG. 27 is a view showing an embodiment of a heat exchanger where anadiabatic plate have the same shape as the cells forming the first fluidcirculation portion is disposed on the inlet side of the first fluid ofa heat exchange element.

DETAILED DESCRIPTION OF THE INVENTION

Hereinbelow, embodiments of the present invention will be described withreferring to drawings. The present invention is not limited to thefollowing embodiments, and changes, modifications, and improvements maybe made as long as they do not deviate from the scope of the invention.

FIG. 1 is a perspective view of a heat exchange element 1 with which aceramics heat exchanger 10 of the present invention is provided. In theheat exchange element 1, the first fluid circulation portions 5 (hightemperature side) each having a honeycomb structure having a pluralityof cells separated by ceramic partition walls 4, extending through inthe axial direction from one end face 2 to the other end face 2, andallowing a heated medium as the first fluid to flow therethrough and thesecond fluid circulation portions 6 (low temperature side) each beingseparated by porous partition walls 4, extending through in thedirection perpendicular to the axial direction, allowing the secondfluid to be circulated, and transferring heat to a medium to be heatedas the second fluid are alternately formed as a unit. The cells 3 on thefirst fluid circulation portion 5 side are smaller than the cells 3 onthe second fluid circulation portion 6 side (In the embodiment of FIG.1, the cells 3 on the second fluid circulation portion 6 side areslits.), and the partition walls 4 have a density of 0.5 to 5 g/cm³ anda thermal conductivity of 10 to 300 W/mK. Making the cells 3 on thefirst fluid circulation portion 5 side smaller than the cells 3 on thesecond fluid circulation portion 6 side is superior to making it largerin terms of heat exchange efficiency. This is because heat can betransferred to the partition walls 4 more easily when the cells 3 forthe first fluid (high temperature side) are small, and the size relationof the cells 3 serves as an important element for heat transfer. Thatis, by constituting the cells 3 on the first fluid circulation portion 5side to be smaller than those on the second fluid circulation portion 6side, heat exchange efficiency can be improved.

Each of the first fluid circulation portions 5 preferably has ahoneycomb structure having a plurality of cells 3 separated by ceramicpartition walls 4 and extending through in the axial direction.

It is preferable that each of the second fluid circulation portions 6has a slit structure having no separating partition wall 4 (partitionwall 14 between slits (see FIG. 3B)) or having small number of (1 to 50)separating partition walls. The second fluid circulation portion 6 isisolated from the first fluid circulation portion 5 by a partition wall4 to be able to transferring heat, and the second fluid circulates in itand receives heat of the first fluid circulating in the first fluidcirculation portions 5 by means of the partition walls 4, thereby heatis transferred to the circulating medium to be heated, which is thesecond fluid.

In the case of honeycomb structure, when the fluid passes through a cell3, the fluid cannot flow into another cell 3 due to the partition walls4 and proceeds linearly from the inlet to the outlet. On the other hand,in the case of a slit structure, for example, the interior of the twoslits as shown in FIG. 3B has no partition wall 4, and slits in the sameline are connected to each other to allow a fluid to pass through to theslit outlet different from the inlet of the fluid. That is, the slits inthe same line are connected to one another in the inside. However, inslits in different lines, fluid cannot pass through because of thepartition wall 4.

The heat exchange element 1 of the present invention is constituted bysegments each having the first fluid circulation portion 5 (hightemperature side) of a honeycomb structure where the first fluid (heatedmedium) circulates and the second fluid circulation portion 6 (lowtemperature side) where the second fluid (medium to be heated) fortransferring heat circulates are formed. For efficient heat exchange, itis more preferable that the first fluid circulation portion 5 has ahoneycomb structure. In the honeycomb structure, a plurality of cells 3functioning as fluid passages are partitioned and formed by thepartition walls 4, and, for the cell shape, a desired shape may suitablybe selected from a circle, an ellipse, a triangle, a quadrangle, otherpolygons, and the like. Incidentally, when a large-sized heat exchangeelement 1 is desired, a module structure where a plurality of segmentsare bonded together can be employed. On the other hand, the second fluidcirculation portion 6 (low temperature side) where the second fluid(medium to be heated) circulates preferably has a slit shape (one orsome in one line), and the shape of the second fluid circulation portion6 is not particularly limited.

Though the shape of the segment of the heat exchange element 1 of thepresent invention is a quadrangular prism, the shape is not limited tothis and may be another shape such as a circular cylindrical shape.

There is no particular limitation on the cell density (i.e., number ofcells per unit cross-sectional area) of the segment, which is a heatexchange element 1 of the present invention, and design may be performedsuitably in accordance with the purpose. However, it is preferably inthe range from 25 to 2000 cells/sq. in. (4 to 320 cells/cm²). When thecell density is below 25 cells/sq. in., the strength of the partitionwalls 4, eventually, the strength of the heat exchange element 1 itself,and effective GSA (geometrical surface area) may be insufficient. On theother hand, when the cell density is above 2000 cells/sq. in., apressure loss when a heat medium flows therethrough may increase.

There is no particular limitation on the thickness of the partitionwalls 4 (wall thickness) of the cells 3 of the honeycomb segment, whichis a heat exchange element 1 of the present invention, and it maysuitably be designed in accordance with the purpose. The wall thicknessis preferably 50 μm to 2 mm, and more preferably 60 to 500 μm. When thewall thickness is smaller than 50 μm, the mechanical strength isdecreased, and breakage may be caused by an impact or thermal stress. Onthe other hand, when it is larger than 2 mm, the rate of the cellcapacity on the honeycomb structure side is lowered, and a defect ofdeterioration in heat exchange rate of permeation of a heating mediummay be caused.

FIG. 2A is a view from an end face 2 in the axial direction of asegment, which is a heat exchange element 1 of an embodiment. As shownin FIG. 2A, the heat exchange element 1 has a plurality of cells 3partitioned by ceramic partition walls 4 and functioning as fluidpassages, and an end face 2 on one side in the axial direction isplugged in every other line. In addition, in the other end face 2, thesame cells 3 as in the end face 2 on the one side are plugged in thesame manner as FIG. 2A. Inside the plugged cells 3, partition walls 4isolating the plugged cells 3 from one another are removed to form aslit shape (see FIG. 3A). That is, in the second fluid circulationportion 6, the end faces 2 in the axial direction are plugged with aplugging material to form plugged portions 13.

FIG. 2B is a view from an end face 2 on one side in the axial directionof a heat exchange element 1 of another embodiment. As shown in FIG. 2B,the heat exchange element 1 has a plurality of cells 3 partitioned byceramic partition walls 4 and functioning as fluid passages, and an endface 2 on one side in the axial direction is plugged in every otherline. In addition, in the other end face 2, the same cells 3 as in theend face 2 on the one side are plugged in the same manner as FIG. 2A.Inside the plugged cells 3, partition walls 4 isolating the pluggedcells 3 from one another are removed to form a slit shape (see FIG. 3A).In the unplugged cells 3, some of the partition walls 4 isolating thecells 3 from one another are removed to form large-sized cells 3. Inother words, the unplugged line is formed to have a honeycomb structurewhere at least one partition wall 4 is present. The constitution as inFIG. 2B is effective for a segment having a long flow passage becausepressure loss of a fluid is smaller. That is, a large amount of thefirst fluid can be allowed to flow.

FIG. 3A show an embodiment viewed from the outer peripheral wall 7 sidewhere slits are formed. As shown in FIG. 3A, in the heat exchangeelement 1, slits extending through from one end face 12 in the directionperpendicular to the axial direction of the outer peripheral wall 7 tothe other end face 12 are formed, and the slits function as the secondfluid circulation portions 6. Each of the slits is formed by removingthe partition walls 4 of the cells 3 plugged in one end face 2 and theother end face 2 in the axial direction. That is, the slits are formedin the same direction as the direction of the cell lines of the pluggedcells 3. The cells 3 unplugged in the end faces 2 are in the state thatthe partition walls 4 are formed as shown in FIG. 2A. Alternatively, asshown in FIG. 2B, there may be employed a constitution where the outerperipheral wall 7 is left and where the partition walls 4 isolating theunplugged cells 3 from one another are removed.

FIG. 3B shows another embodiment viewed from the outer peripheral wall 7side where slits are formed. As shown in FIG. 3B, in the heat exchangeelement 1, slits extending through from one end face 12 in the directionperpendicular to the axial direction of the outer peripheral wall 7 tothe other end face 12 are formed, and an inter-slit partition wall 14separating the slits is formed in the center in the axial direction.Incidentally, the inside of the inter-slit partition wall 14 has a shapewhere partition walls of the cells 3 remain. This makes the structure ofthe heat exchange element 1 itself strong. Therefore, the heat exchangeelement 1 hardly breaks. When the slits are long, strength is reduced,and breakage may be caused. However, by forming the inter-slit partitionwall 14, in other words, by leaving the cell wall faces, increase instrength can be planned. The slits are formed by removing the partitionwalls 4 of the cells 3 plugged in one end face 2 on one side and theother end face 2 on the other side in the axial direction, and the cells3 unplugged in the end faces 2 are as shown in FIGS. 2A and 2B like theaforementioned embodiment.

It is preferable that the segment, which is a heat exchange element 1,employs ceramics excellent in thermal resistance, in particular, siliconcarbide in consideration of conductivity. However, it is not alwaysnecessary that the entire segment of the heat exchange element 1 isconstituted of silicon carbide as long as silicon carbide is containedin the main body. That is, it is preferable that the heat exchangeelement 1 of the present invention is of conductive ceramics containingsilicon carbide. As a property of a segment of the heat exchange element1, the thermal conductivity at room temperature is preferably 10 W/mK orhigh, and 300 W/mK or low. However, it is not limited to the range. Itis possible to use a corrosion resistant metal material such as aFe—Cr—Al base alloy in place of the conductive ceramics.

The density of the partition walls 4 of the cells 3 of the heat exchangeelement 1 is preferably 0.5 to 5 g/cm³. In the case that it is below 0.5g/cm³, the partition walls 4 have insufficient strength and may breakdue to pressure when the first fluid passes through the flow passages.In addition, when it is above 5 g/cm³, the heat exchange element 1itself becomes heavy, and the characteristic of weight saving may beimpaired. By the density in the aforementioned range, the heat exchangeelement 1 can be made strong. In addition, the effect in improving thethermal conductivity can be obtained.

In order that the heat exchange element 1 of a ceramics heat exchanger10 of the present invention may obtain high heat exchange rate, it ispreferable to use a material containing silicon carbide having highthermal conductivity as the material for the segment. However, sincehigh thermal conductivity cannot be obtained in the case of a porousbody even by silicon carbide, it is more preferable to obtain a densebody structure by impregnating the segment as the heat exchange element1 with silicon in the process of producing the segment. By the densebody structure, high thermal conductivity can be obtained. For example,in the case of porous body of silicon carbide, it is about 20 W/mK.However, by the dense body, it can be made about 150 W/mK.

That is, though Si-impregnated SiC, Si₃N₄, SiC, or the like may beemployed as the ceramic material, it is particularly desirable to employSi-impregnated SiC in order to obtain a dense body structure forobtaining high heat exchange rate. Since the Si-impregnated SiC has astructure where a coagulation of metal silicon melt surrounds thesurfaces of the SiC particles and where SiC particles are unitarilybonded together by means of metal silicon, silicon carbide is blockedfrom the atmosphere containing oxygen to be inhibited from beingoxidized. Further, though SiC has the characteristics of high thermalconductivity and easy heat release, Si-impregnated SiC is formed denselywith showing high thermal conductivity and heat resistance and showssufficient strength as a heat transfer member. That is, the heatexchange element 1 of a Si—SiC based (Si-impregnated SiC) material showshigh thermal conductivity as well as properties excellent in corrosionresistance against acid and alkali besides thermal resistance, thermalshock resistance, and oxidation resistance.

More specifically, in the case that the heat exchange element 1 containsa Si-impregnated SiC composite material as the main component, when theSi content specified by Si/(Si+SiC) is too small, the bonding materialbecomes insufficient. Therefore, bonding of adjacent SiC particles bythe Si phase becomes insufficient to lower the thermal conductivity andto have a difficulty in obtaining strength capable of maintaining thethin wall structure such as a honeycomb structure. Inversely, when theSi content is too large, the heat exchange element 1 is excessivelycontracted by firing due to the presence of metal silicate in the amountwhere the SiC particles can suitably be bonded or more to cause negativeeffects such as decrease in porosity and reduction in average porediameter, which is not preferable. Therefore, the Si content ispreferably 5 to 50 mass %, more preferably 10 to 40 mass %.

In such Si-impregnated SiC, pores are filled with metal silicon, andthere is a case that the porosity is 0 or nearly 0. It is excellent inoxidation resistance and durability and can be used for a long period oftime in a high temperature atmosphere. Once it is oxidized, since anoxidation protection film is formed, oxidation deterioration is notcaused. In addition, since it has high strength from ordinarytemperature to high temperature, a thin and light weight structure canbe formed. Further, it has high thermal conductivity which is about thesame as that of copper or aluminum metal, high far-infrared emissivity,and electrical conductivity, thereby hardly having static electricity.

In the case that the first fluid (high temperature side) allowed tocirculate in a ceramics heat exchanger 10 of the present invention isexhaust gas, it is preferable that a catalyst is loaded on the wallsurfaces inside the cells 3 of the heat exchange element 1 where thefirst fluid (high temperature side) passes. This is because it canexchange also reaction heat (exothermic reaction) generating uponexhaust gas purification in addition to the role of exhaust gaspurification. The catalyst preferably contains at least one elementselected from the group consisting of noble metals (platinum, rhodium,palladium, ruthenium, indium, silver, and gold), aluminum, nickel,zirconium, titanium, cerium, cobalt, manganese, zinc, copper, zinc, tin,iron, niobium, magnesium, lanthanum, samarium, bismuth, and barium.These may be metals, oxides, and other compounds. The amount of thecatalyst (catalyst metal and carrier) loaded on the first fluidcirculation portion 5 of the heat exchange element 1 where the firstfluid (high temperature side) passes is preferably 10 to 400 g/L. In thecase of a noble metal, the amount is further preferably 0.1 to 5 g/L.When the amount of the catalyst (catalyst metal and carrier) is below 10g/L, it may be difficult to exhibit the catalyst function. On the otherhand, when the amount is above 400 g/L, pressure loss increases, and theproduction costs may increase. As necessary, a catalyst is loaded on thepartition walls 4 of the cells 3 of the heat exchange element 1. In thecase of loading the catalyst, a mask is applied on the segment, which isa heat exchange element 1, to allow the catalyst to be loaded on theheat exchange element 1. After a ceramic powder functioning as carriermicroparticles is impregnated with an aqueous solution containing acatalyst component in advance, drying and firing are performed to obtaincatalyst-coated microparticles. To the catalyst-coated microparticlesare added a dispersion medium (water or the like) and other additives toprepare a coating liquid (slurry), and, after the slurry is coated onthe partition walls 4 of the heat exchange element 1, drying and firingare performed to load the catalyst on the partition walls 4 of the cells3 of the heat exchange element 1. Incidentally, upon firing, the mask ofthe heat exchange element 1 is peeled off.

As shown in FIG. 4, a ceramics heat exchanger 10 of the presentinvention may have a structure where a plurality of segments functioningas heat exchange elements 1 are bonded together with a bonding materiallayer 8 of heat resistant cement. A large size can be obtained bymodularization by bonding segments functioning as the heat exchangeelements 1 of the present invention. The segments are bonded by the useof heat resistant cement. The heat resistant cement plays a role of anadhesive and is applied to the periphery of the face where the inflowport and the outflow port of the second inflow circulation portion 6 areformed of the outer peripheral walls 7 of the segments to bond segmentstogether. In this case, the bonding material is applied lest the secondfluid circulation portion 6 should be closed by the heat resistantcement.

As shown in FIG. 5, a ceramics heat exchanger 10 of the presentinvention includes a heat exchange element 1 and a heat exchangeelement-holding container 11 having the heat exchange element 1 therein.Though the material of the heat exchange element-holding container 11 isnot particularly limited, the container is preferably constituted of ametal having good workability (e.g. stainless steel). The material forthe constitution including a connection pipe is not particularlylimited.

FIG. 6 shows another embodiment of a heat exchange element 1 and is aview from the end face 2 on the one side, which is the first fluid inletside of a heat exchange element 1. As shown in FIG. 6, the heat exchangeelement 1 has a plurality of cells 3 separated by ceramic partitionwalls 4, extending through in the axial direction from one end face 2 onone side to the end face 2 on the other side (see FIG. 1), and allowingthe heating element functioning as the first fluid to circulatetherethrough. Some of the partition walls 4 forming the cells 3 havedifferent thickness (wall thickness). That is, the heat exchange element1 of FIG. 1 is an embodiment where the partition walls 4 have thickportions and thin portions. The constitution other than the thickness ofthe partition walls 4 is the same as the heat exchange element 1 of FIG.1 and is formed in such a manner that the second fluid circulatesperpendicularly to the first fluid. By such a difference in wallthickness, pressure loss can be reduced. Incidentally, the thickportions and the thin portions of the walls may be disposed regularly orat random as shown in FIG. 6, and similar effects can be obtained.

FIG. 7A shows an embodiment where an end face 2 of the partition wall 4of the heat exchange element 1 is a tapered face 2 t and is a view ofthe end face 2 on one side of the heat exchange element 1 from the firstfluid inlet side. FIG. 7B shows an embodiment where an end face 2 of thepartition wall 4 of the heat exchange element 1 is a tapered face 2 tand is a cross sectional view taken along the face in parallel with theaxial direction. As shown in FIGS. 7A and 7B, the heat exchange element1 has a plurality of cells 3 partitioned by ceramic partition walls 4and extending through in the axial direction from one end face 2 to theother end face 2 (see FIG. 1), and allowing a heated medium functioningas the first fluid to circulate therethrough with the end face 2 being atapered face 2 t. By making the end portion of the partition wall 4 ofthe inlet of the first fluid have a tapered face 2 t, the inflowresistance of the fluid is decreased to reduce pressure loss.

FIG. 8A is a view of the end face 2 viewed from the first fluid inletside of the heat exchange element 1, showing an embodiment where thecells 3 having different sizes are formed. FIG. 8B is a decompositionperspective view of the embodiment of FIG. 8A. Since the first fluidflowing the central portion has a high flow rate, the temperature ishigh, the volume is large, and the pressure loss is large. Therefore, bymaking the cells 3 in the central portion large, the pressure loss canbe reduced. In the embodiments shown in FIGS. 8A and 8B, a honeycombstructure having large-sized cells 3 partially including pluggedportions 13 is disposed in the central portion, and the outer peripheralwall is provided with a fluid sealing material 19 in the end portionthereof. Four honeycomb structures 4 having small-sized cells partiallyincluding plugged portions 13 are provided to surround the outerperiphery of the honeycomb structure in the central portion. It allowsthe second fluid to flow from the second fluid circulation portion 6 ofthe outside honeycomb structure to the second fluid circulation portion6 of the inside (central portion) honeycomb structure by the fluidsealing material 19.

FIG. 8C is a decomposition perspective view showing an embodiment of acircular cylindrical heat exchange element 1 having the cells 3 havingdifferent sizes and partially including plugged portions 13. Each of theinside circular columnar honeycomb structure and the outside circularhoneycomb structure has the first fluid circulation portion 5 and thesecond fluid circulation portion 6 formed therein (Cells 3 are pluggedsimilarly to, for example, FIG. 2A, and each circulation portion isformed.), and a fluid sealing material 19 is unitarily provided betweenthe inside circular cylindrical honeycomb structure and the outsidecylindrical honeycomb structure. (FIG. 8C shows the inside honeycombstructure and the outside honeycomb structure in the decomposed state.)The fluid sealing member 19 enables the second fluid to flow from thesecond fluid circulation portion 6 of the outside honeycomb structure tothe second fluid circulation portion 6 of the inside honeycombstructure.

FIG. 8D shows an embodiment where the cells 3 have different sizes andis a view of an end face 2 from the inlet side of the first fluid. Theembodiment is formed so that the size of the cells 3 gradually increasesfrom the right side to the left side of the figure. The right side ofthe figure is the inlet side of the second fluid, and the cells 3 aresmall on the inlet side of the second fluid inlet side while the cells 3are large on the outlet side. In the heat exchanger 10 shown in FIG. 5,when the first fluid circulation portion is formed as FIG. 8D withsending the second fluid from the right side to the left side of FIG.8D, since the temperature of the second fluid is high in the downstreamside (left side of FIG. 8D) of the second fluid, the temperature of thefirst fluid flowing on the down stream side of the second fluid becomeshigh, and pressure loss is large. However, by enlarging the cells 3 onthe down stream side of the second fluid, pressure loss can be reduced.FIG. 8E shows an embodiment where the thickness of the partition walls 4of the cells 3 is changed and is a view of the end face 2 on the inletside of the first fluid. The partition walls 4 are formed so that thethickness gradually reduces from the right side to the left side of thefigure. The right side of the figure is the inlet side of the secondfluid, and, by thinning the partition walls 4 of the cells 3 on thedownstream side of the second fluid, the pressure loss can be decreasedlike the case of FIG. 8D.

FIG. 9A is a cross-sectional view taken along a cross section inparallel with the axial direction, showing an embodiment of a heatexchange element 1 where the thickness of the partition walls 4 isincreased from the inlet side of the first fluid toward the outlet side(from the upstream side to the downstream side). In addition, FIG. 9Bshows an embodiment of a heat exchange element 1 where the first fluidcirculation portions 5 are gradually narrowed from the inlet side of thefirst fluid toward the outlet side (from the upstream side to thedownstream side). In the first fluid circulation portions 5, temperatureof the first fluid falls, and heat transfer is reduced by the volumecontraction of the first fluid as it flows toward the downstream side.By narrowing the first fluid circulation portions 5, contact isimproved, and heat transfer between the first fluid and the wall facesof the partition walls can be increased.

In a heat exchange element 1 shown in FIG. 1, the shape of the cells 3functioning as the first fluid circulation portion 5 may be madehexagonal as shown in FIG. 10A. In addition, as shown in FIG. 10B, theshape of the cells 3 of the first fluid circulation portion 5 may bemade octagonal. By such a shape, since the angle of the corners iswidened, stagnation or the like of the fluid is reduced, and boundaryfilm thickness (temperature boundary layer thickness of the first fluid)can be reduced to raise the heat transfer coefficient between the firstfluid and the wall faces of the partition walls.

In addition, in a heat exchange element 1 shown in FIG. 1, as shown inFIG. 11, the R portion 3 r may be formed by making the corner portion ofthe cell 3 functioning as the first fluid circulation portion 5 have anR shape. By such a shape, since the angle of the corners is widened,stagnation or the like of the fluid is reduced, and boundary filmthickness can be reduced to raise the heat transfer coefficient betweenthe first fluid and the wall faces of the partition walls.

Further, in the heat exchange element 1 shown in FIG. 1, as shown inFIGS. 12A and 12B, there may be employed a fin structure having fins 3 fprotruding in the cells 3 functioning as the first fluid circulationportion 5. The fins 3 f are formed so as to extend in the axialdirection (direction where the first fluid flows) on wall faces ofpartition walls 4 forming the cell 3, and the shape of each fin 3 f maybe a plate-like shape, a semispherical shape, a triangle, a polygon, orthe like. This enables not only to increase the conductive area, butalso thin the boundary film by disarranging the flow to raise the heattransfer coefficient between the first fluid and the wall faces of thepartition walls. Incidentally, the fins 3 f may be formed only inunplugged cells 3 or in plugged cells 3.

FIG. 13A shows an embodiment of a heat exchange element 1 where a partof the cell structure is dense. FIG. 13B is a decomposition perspectiveview of the embodiment of FIG. 13A. The first fluid flowing in the cells3 in the central portion of the heat exchange element 1 has hightemperature because of a high flow rate. It is preferable to narrow thecells in the central portion of the heat exchange element 1 and to widenthe cells 3 in the external side portion of the heat exchange element 1.In the embodiment shown in FIGS. 13A and 13B, a honeycomb structurehaving small-sized cells 3 partially including plugged portions 13 isdisposed in the central portion, fluid sealing materials 19 are providedin the end portions of the outer peripheral walls, and four honeycombstructures 4 having large-sized cells 3 partially including pluggedportions 13 are provided so as to surround the outer periphery of thehoneycomb structure in the central portion. The fluid sealing materials19 enable the second fluid to flow from the second fluid circulationportion 6 of the outside honeycomb structure to the second fluidcirculation portion 6 of the inside (central portion) honeycombstructure.

FIG. 13C is a decomposition perspective view showing an embodiment of acircular cylindrical heat exchange element where cells 3 partiallyincluding plugged portions 13 and having different sizes. Each of theinside circular columnar honeycomb structure and the outside circularhoneycomb structure has the first fluid circulation portion 5 and thesecond fluid circulation portion 6 formed therein (Cells 3 are pluggedsimilarly to, for example, FIG. 2A, and each circulation portion isformed.), and a fluid sealing material 19 is unitarily provided betweenthe inside circular cylindrical honeycomb structure and the outsidecylindrical honeycomb structure. (FIG. 13C shows the inside honeycombstructure and the outside honeycomb structure in the decomposed state.)The fluid sealing member 19 enables the second fluid to flow from thesecond fluid circulation portion 6 of the outside honeycomb structure tothe second fluid circulation portion 6 of the inside honeycombstructure.

FIG. 13D is an embodiment where a part of the cell structure is denselyformed, viewed form the end face 2 on the inlet side of the first fluid.The structure is formed so that cell density may gradually increase fromthe right side of the figure to the left side. In the cells 3functioning as the first fluid circulation portion 5, the cell densityon the second fluid inlet side is low, and the cell density on theoutlet side is high. In addition, FIG. 13E shows an embodiment of a heatexchange element 1 where the cell structure is changed by changing thethickness (wall thickness) of the partition walls 4. The cells 3functioning as the first fluid circulation portions 5 have low celldensity on the inlet side of the second fluid on the right side of thefigure and high cell density of the outlet side on the left side of thefigure. In the heat exchange element 1 shown in FIG. 5, by forming thefirst fluid circulation portion 5 as in FIG. 13D (or FIG. 13E) to allowthe second fluid to flow from the right side to the left side of FIG.13D (or FIG. 13E), the first fluid flowing on the second fluiddownstream side (left side of FIG. 13D (or FIG. 13E)) has hightemperature because the second fluid has high temperature and has highpressure loss. However, by raising the cell density on the downstreamside of the second fluid of the cells 3 of the first fluid circulationportion 5, the conductive area can be increased. In addition, byincreasing the thickness of the partition walls 4, the total heattransfer amount can be increased.

FIG. 14A shows an embodiment of a heat exchanger 10 where a plurality ofheat exchange elements 1 are disposed in series in the direction wherethe first fluid flows and where the direction of the partition walls 4forming the cells 3 of the front part (upstream side) heat exchangeelement 1 and the direction of the partition walls 4 forming the cells 3of the rear part (downstream side) heat exchange element 1 are offset.In the present embodiment, cells 3 are plugged similarly to the case of,for example, FIG. 2A with each circulation portion being formed. FIG.14B shows an embodiment of a heat exchanger 10 with the positions of thepartition walls 4 being offset. Thus, by allowing the heat exchanger 10to have a structure where the directions, positions, and the like ofpartition walls 4 of a plurality of the heat exchange elements 1 areoffset, the flow of the fluid can be disarranged at the sites where thepositions of the walls are offset, and boundary film thickness can bereduced to raise the heat transfer coefficient between the first fluidand the wall faces of the partition walls.

FIG. 15 shows an embodiment of a heat exchanger 10 having a constitutionwhere a plurality of heat exchange elements 1 are disposed in series inthe direction where the first fluid flows and where the cell density ofthe rear part (downstream side) heat exchange element 1 is higher thanthat of the front part (upstream side) heat exchange element 1. In thepresent embodiment, cells 3 are plugged similarly to the case of, forexample, FIG. 2A with each circulation portion being formed. In thefirst fluid circulating in the first fluid circulation portion 5,temperature falls as it flows downstream, and heat transfer is reducedby volume contraction of the first fluid. In the present embodiment, bythe disposition where the rear part (downstream) heat exchange element 1has higher cell density, conductive area is increased to improve heattransfer between the first fluid and the wall faces of the partitionwalls 4.

FIG. 16 shows an embodiment of a heat exchanger 10 where a plurality ofheat exchange elements 1 having regions having different cell densitydistributions are disposed in series in a direction where the firstfluid flows. Each of the heat exchange elements 1 has a constitutionshown by any of FIGS. 8C and 13C. Specifically, the embodiment has aconstitution where two regions of the inside (center side) and the outerperiphery side in a peripheral direction are formed and where the celldensity of the front part (upstream) heat exchange element 1 is high inthe inside and low in the outer periphery side while the cell density ofthe rear part (downstream) heat exchange element 1 is low in the insideand high in the outer periphery side. By allowing the fluid flow to bedisarranged by the cell structure where the cell density distribution ischanged between the front part and the rear part, boundary filmthickness can be reduced to raise the heat transfer coefficient betweenthe first fluid and the wall faces of the partition walls 4.Incidentally, the number of regions having different cell densities isnot limited to two and may be three or more.

FIG. 17A shows an embodiment of a heat exchanger 10 where a plurality ofheat exchange elements 1 each having regions partially including pluggedportions 13 and having different cell density distributions formedtherein are disposed in series in the direction where the first fluidflows. FIG. 17B is a decomposition perspective view of the embodiment ofFIG. 17A. In the present embodiment, cells 3 in each region are pluggedsimilarly to, for example, the case of FIG. 2A with each circulationportion being formed. Specifically, two semicircular regions are formed,and, upon disposing honeycomb structures as the heat exchange elements 1in series, the cell density distributions are changed between the leftand the right (or the top and the bottom) of the front part (upstream)and rear part (downstream) honeycomb structures. The embodiment has aconstitution where the cell density of the front part heat exchangeelement 1 is high on one side (right side in the figure) and low in theother side (left side in the figure), and the cell density of the rearpart heat exchange element 1 is high on the other side (left side in thefigure) and low in the one side (right side in the figure). That is,since the cell density in the corresponding portions is differentbetween the front part heat exchange element and the rear part heatexchange element, in other words, because of a cell structure where thecell density distribution is changed between the front part one and therear part one, the fluid flow can be disarranged, and boundary filmthickness can be reduced to raise the heat transfer coefficient betweenthe first fluid and the wall faces of the partition walls 4. As shown inFIG. 17C, there may be employed a heat exchange element 1 having ahoneycomb structure where quadrangular two regions are formed. By theconstitution where the cell density distribution is changed between theleft and the right (or the top and the bottom) of the front part(upstream) and rear part (downstream) honeycomb structures upondistributing the heat exchange elements 1 shown in FIG. 17C in series asin FIG. 17A, the fluid flow can be disarranged, and the heat transfercoefficient can be raised.

FIG. 18A shows an embodiment of a heat exchanger 10 having aconstitution where a plurality of heat exchange elements 1 are disposedin series in the direction where the first fluid flows and where theflow passages of the first fluid are changed between the front part oneand the rear part one. Specifically, two regions of the inside (centerside) and the outer periphery side are formed in a peripheral direction,the front part heat, exchange element 1 is entirely plugged in the outerperiphery side and partially plugged in the inside (Cells 3 in theinside are plugged similarly to, for example, the case of FIG. 2A witheach circulation portion being formed.), and the rear part heat exchangeelement 1 is entirely plugged in the inside and partially plugged in theouter periphery side (Cells 3 in the outer periphery side are pluggedsimilarly to, for example, the case of FIG. 2A with each circulationportion being formed.) By such constitution, the fluid low can bedisarranged, and boundary film thickness can be reduced to raise theheat transfer coefficient between the first fluid and the wall faces ofthe partition walls. FIG. 18B is a view showing an embodiment of a heatexchanger where heat exchange elements 1 each obtained by combining anentirely plugged prismatic column and a partially unplugged prismaticcolumn are disposed in the front part and rear part portions. The bottomregion of the front part is completely plugged, and the upper region ofthe rear part is completely plugged. The constitution enables the flowof the first fluid to change.

FIG. 19A shows an embodiment of a heat exchange element 1 where theinlets and the outlets of the first fluid circulation portions 5 arealternately plugged. FIG. 19B is an A-A cross-sectional view in FIG.19A. The material for the partition walls 4 is varied depending on theplace of the partition walls 4, and the constitution is made so that thefirst fluid flowing in from the inlet passes the partition walls 4 andflows out from the outlet. By the constitution, heat collection of thefirst fluid is performed not on the wall face but inside the porouspartition walls 4. Since heat can be collected not by thetwo-dimensional surface but three-dimensionally, the conductive area canbe increased.

FIG. 20 shows an embodiment where porous walls 17 are formed in thefirst fluid circulation portion 5 as the first fluid passage. FIG. 20 isa cross-sectional view of the first fluid circulation portion 5. Theporosity of the porous walls in the first fluid circulation portion 5 ishigher than that of the partition walls 4 between the first fluidcirculation portion 5 and the second fluid circulation portion 6.Therefore, in the present embodiment, the first fluid passes through theporous walls 17 and is discharged from the outlet. Since heat can becollected not by the two-dimensional surface but three-dimensionally,the conductive area can be increased even in the same volume.Alternatively, the heat exchange element 1 can be miniaturized.

FIG. 21 shows an embodiment of a heat exchange element 1 where thethickness (wall thickness) of the partition walls 4 forming the firstfluid circulation portion 5 is gradually increased from the centertoward the outer periphery in a cross section perpendicular to the axialdirection. In the case of the heat exchange elements having the samesize, the thicker the wall is, the higher the fin efficiency is. Bythickening the path for transferring heat collected from the cellcentral portion, heat conduction inside the wall can be increased.

FIG. 22 shows an embodiment of a heat exchange element 1 employing ahoneycomb structure having an external shape of an ellipse. In thepresent embodiment, the partition walls 4 extending in the short axialdirection is formed to be thick. Since the fin efficiency is high as thepartition walls 4 became thick, thick walls are disposed on the sideperpendicular to the second fluid so that the heat of the first fluidcan be transferred to the second fluid to raise the entire thermalconduction. In addition, pressure loss can be reduced in comparison withincrease of the thickness in the entire portions. The shape of the heatexchange element 1 may be rectangle.

FIG. 23 shows an embodiment where the outer peripheral wall 7 of ahoneycomb structure forming the heat exchange element 1 is thicker thanthe partition walls 4 forming the cells 3. By making the outerperipheral wall 7 thicker than the cells 3 in the central portion,strength of the structure can be enhanced. In the present embodiment,the cells 3 are plugged similarly to, for example, the case of FIG. 2Awith each circulation portion being formed.

FIG. 24 shows an embodiment where the external shape of the honeycombstructure forming the heat exchange element is flattened. The conductivepath can be made short in the short axial portion in comparison with acircle, and it has small waterway pressure loss in comparison with thecase of making the external shape of the honeycomb structure a cornerstructure.

FIGS. 25A to 25C show an embodiment where end faces 2 on the inlet sideof the first fluid of the honeycomb structure are inclined. By incliningthe inlet, the area where the high temperature portion of the firstfluid is brought into contact becomes wider to increase the entireconductive area. It is also possible to make the end faces on the outletside inclined, and, in this case, the pressure loss can be reduced.

FIG. 26 shows an embodiment where the end face 2 on the inlet side ofthe first fluid of the honeycomb structure forming a heat exchangeelement 1 is formed to have a depressed face shape. By making the inletof the first fluid depressed, the high temperature portion of the firstfluid is extended backward to raise the heat exchange efficiency of thehoneycomb backward portion with the second fluid. In addition, by makingthe depression, the thermal stress at the surface can be made acompression stress to be able to maintain high rupture strength.

FIG. 27 shows an embodiment of a heat exchanger 10 where an adiabaticplate 18 has the same shape as the cells 3 forming the first fluidcirculation portion 5 is disposed on the inlet side of the first fluidof a heat exchange element 1. Since the opening ratio of the inlet onthe first fluid side is small, in the case of disposing no adiabaticplate, when the first fluid is brought into contact with the end face onthe inlet side, heat is lost at the inlet wall face. Disposing anadiabatic plate having the same shape in accordance with the inletallows the first fluid to flow into the honeycomb with maintaining theheat to prevent the heat of the first fluid from being lost. In thepresent embodiment, cells 3 are plugged similarly to, for example, thecase of FIG. 2A with each circulation portion being formed.

There is no particular limitation on the heated medium as the firstfluid being circulated in a ceramics heat exchanger 10 of the presentinvention having a constitution as described above as long as it is amedium having heat, such as gas or liquid. An example of gas isautomobile exhaust gas. In addition, regarding the medium to be heatedas the second fluid which take heat from (exchange heat with) the heatedmedium, there is no particular limitation on the medium as long as thetemperature is lower than that of the heated medium, such as gas orliquid. Though water is preferable in consideration of handling, it isnot particularly limited to water.

As described above, since the heat exchange element 1 has high heatconductivity, and there is a plurality of sites functioning as fluidpassages by the partition walls 4, high heat exchange rate can beobtained. Therefore, the entire heat exchange element 1 can beminiaturized, and it can be mounted on an automobile. In addition,pressure loss is small with respect to the first fluid (high temperatureside) and the second fluid (low temperature side).

Next, a method for manufacturing a ceramics heat exchanger 10 of thepresent invention is described. In the first place, a ceramic formingraw material is extruded to form a honeycomb structure where a pluralityof cells 3 partitioned by ceramic partition walls 4 and extendingthrough in an axial direction from one end face 2 to the other end face2 are partitioned and formed. Then, regarding a part of the cell lines,slits are formed so as to extend through the partition walls 4 formingthe cells 3 and the outer peripheral wall 7 of the honeycomb structurein the direction perpendicular to the axial direction, and pluggedportions 13 plugged with plugging members are formed on one end face 2each of and the other end face 2 of each of the cells 3 in the celllines where the slits are formed to manufacture a heat exchange element1.

Specifically, the manufacturing can be performed as follows. Afterkneaded clay containing a ceramic powder is extruded into a desiredshape, drying and firing are performed to obtain a honeycomb structuresegment. By this, there can be obtained a honeycomb structure segment(rectangular parallelepiped) where a plurality of cells 3 functioning asgas flow passages are partitioned and formed by the partition walls 4.

Though the aforementioned ceramics can be employed as the material forthe heat exchange element 1, for example, in the case of manufacturing asegment containing Si-impregnated SiC composite material as the maincomponent, in the first place, predetermined amounts of a C powder, aSiC powder, a binder, and water or an organic solvent are kneaded andformed to obtain a formed article having a desired shape. Next, theformed article is put in pressure-reduced inert gas or vacuum in a metalSi atmosphere to impregnate the formed article with metal Si.

Incidentally, also, in the case of employing Si₃N₄, SiC, and the like,kneaded clay of a forming material is formed, and the kneaded clay issubjected to extrusion forming in a forming step to form ahoneycomb-shaped formed article having a plurality of cells 3partitioned by partition walls 4 and functioning as exhaust gaspassages. The article is dried and fired to obtain a heat exchangeelement 1 of a segment formed as a honeycomb structure (honeycombstructure segment).

Next, the honeycomb structure segment manufactured above is cut out toform slits in every other cell line on the side of the honeycombstructure segment. Then, with respect to the cut-out face (end face 2)on the honeycomb structure side, plugging on each cell line having aslit is performed. The plugging material preferably has the samecomposition as that of the honeycomb structure segment. When the segmentis of silicon carbide (SiC), the plugging material is preferably ofsilicon carbide. Then, the plugged honeycomb structure (segment) isfired in a hydrogen atmosphere to manufacture a segment as a heatexchange element 1.

As described above, a side face (outer peripheral wall 7) of thehoneycomb-structured segment manufactured by extrusion forming asdescribed above is subjected to slit-working to form the second fluidcirculation portions 6, and the first fluid circulation portions 5 aresubjected to plugging for manufacturing at low costs. When the size ofthe heat exchange element 1 is increased, modularization is easy.

Since a heat exchange element 1 of the present invention has across-flow structure of the first fluid (high temperature side) and thesecond fluid (low temperature side) and shows high heat exchangeefficiency between the first fluid (high temperature side) and thesecond fluid (low temperature side) in comparison with conventionalones, the heat exchanger 10 itself can be miniaturized. Further, sincemanufacturing from a unitary type by extrusion forming is possible,costs can be reduced. The heat exchange element 1 can suitably be usedin the case that the first fluid is gas and that the second fluid isliquid. For example, it can suitably be used for exhaust heat recoveryor the like to improve automobile gas mileage.

EXAMPLE

Hereinbelow, the present invention will be described in more detail onthe basis of Examples. However, the present invention is by no meanslimited to these Examples.

(Manufacturing of Segment of Heat Exchange Element)

After the kneaded clay containing a ceramic powder was extruded to havea desired shape, it was dried and fired to manufacture a heat exchangeelement 1 of silicon carbide segment having a main body size of 33×33×60mm.

Examples 1 to 5 Comparative Examples 1 to 3

The structures of the segments of the heat exchange elements 1 ofExamples 1 to 5 and Comparative Examples 1 to 3 are as in Table 1.Incidentally, no catalyst was loaded on any of the Examples andComparative Examples. In addition, the “number of the partition walls”of the first fluid circulation portion 6 shows the number of thepartition walls in one line (For example, the numbers of the partitionwalls are “6” in FIG. 2A and “2” in FIG. 2B.).

(Heat Exchange Element-Holding Container)

As the outside container for the heat exchange element 1, a stainlesssteel heat exchange element-holding container 11 was used. Pipes areprovided on the heat exchange element-holding container 11 in accordancewith the cross-flow structure of the heat exchange element 1.Incidentally, the two routes are completely partitioned lest the firstfluid and the second fluid should be mixed together.

(First Fluid and Second Fluid)

The inlet temperature and the flow rate of the first fluid and thesecond fluid were entirely the same. As the first fluid, nitrogen gas(N₂) at 350° C. was used. As the second fluid, water was used.

(Test Method)

The nitrogen gas had a SV (space velocity) of 50,000 h⁻¹ with respect tothe heat exchange element 1. Model gas was allowed to flow into thefirst fluid circulation portions 5 of the heat exchange element 1, and(cooled) water was sent into the second fluid circulation portions 6.The (cooled) water had a flow rate of 5 L/min. Though the heat exchanger10 of Comparative Example 1 has a structure different from those of theheat exchangers 10 of Examples 1 to 3, the test conditions such as flowrate of the first fluid and the second fluid were entirely the same.Incidentally, the pipe capacity (portion of the heat exchange element 1)of Comparative Example 1 was the same as the main body capacity (33 cc)of the segments of heat exchange elements 1 of Examples 1 to 3.Comparative Example 1 had pipes having a dual structure where the secondfluid flow passage is present in the outer peripheral portion of thepipe functioning as the first fluid flow passage. That is, it had astructure where the second fluid flows outside the pipe for the firstfluid. It had a structure where the (cooling) water flows outside (gapof 5 mm) the pipe. The pipe capacity of Comparative Example 1 meanscapacity of the pipe functioning as the first fluid flow passage.

(Test Result)

Table 1 shows heat exchange rate. The heat exchange rate (%) wasobtained by calculating each energy amount from the ΔT° C. (outlettemperature of heat exchange element−inlet temperature) of each of thefirst fluid (nitrogen gas) and the second fluid (water) with the formula1.

Heat exchange rate(%)=temperature rise energy amount of medium to beheated (second fluid)/temperature fall energy amount of heated medium(first fluid)  (formula 1)

TABLE 1 Heat exchange element Partition wall First fluid circulationSecond fluid Partition wall thermal Heat exchange portion (number ofcirculation density conductivity efficiency Material Shape partitionwalls) portion Route (g/cm³) (W/mK) (%) Example 1 Silicon carbideSegment Honeycomb structure Slit structure Cross flow 0.5 10 85 (6partition walls) structure Example 2 Silicon carbide Segment Honeycombstructure Slit structure Cross flow 1.5 23 88 (6 partition walls)structure Example 3 Silicon carbide Segment Honeycomb structure Slitstructure Cross flow 1.5 23 84 (2 partition walls) structure Example 4Silicon carbide Segment Honeycomb structure Slit structure Cross flow3.0 150 92 (densification by (6 partition walls) structure Siimpregnation) Example 5 Silicon carbide Segment Honeycomb structure Slitstructure Cross flow 5.0 300 96 (densification by (6 partition walls)structure Si impregnation) Comp. Ex. 1 SUS304 Piping structure Outsideof Outer periphery 7.5 15 79 structure flow structure Comp. Ex. 2Silicon carbide Segment Honeycomb structure Slit structure Cross flow0.3 8 Broken during (6 partition walls) structure test Comp. Ex. 3Silicon cargide Segment Honeycomb structure Slit structure Cross flow5.1 320 Broken during (densification by (6 partition walls) structureproduction Si impregnation)

Comparison of Examples 1 to 3 with Comparative Example 1

As shown in Table 1, Example 1 showed high heat exchange efficiency incomparison with Comparative Example 1. This seems to be because, in thecase of Comparative Example 1, though heat exchange with the first fluid(nitrogen gas) was easy on the side close to (cooling) water, sufficientheat exchange was hard in the central portion of the pipe, and therebythe thermal exchange rate was low as a whole. On the other hand, sincethe present invention has a honeycomb structure, the wall area where thefirst fluid (nitrogen gas) is brought into contact with (cooling) wateris large in comparison with Comparative Example 1, and this seems to bethe cause of high heat exchange efficiency.

Comparison of Example 2 with Example 3

As shown in Table 1, Example 2 had high heat exchange efficiency incomparison with Example 3. This shows that a honeycomb structure havingmore partition walls (Example 2) is more excellent in heat exchange thana honeycomb structure having less partition walls, and this seems to bebecause the wall area where the first fluid is brought into contactincreases by a honeycomb structure having more partition walls.

Comparison of Examples 1 to 3 with Examples 4 and 5

As shown in Table 1, Examples 4 and 5 had high heat exchange efficiencyin comparison with Examples 1 to 3. This seems to be because Examples 4and 5 became dense bodies by impregnation of the segment of the heatexchange element 1 with Si to raise thermal conductivity. This showsthat performing Si impregnation is more preferable.

Comparison of Example 1 with Comparative Example 2

As shown in Table 1, Example 1 had no breakage of partition walls duringthe test evaluation in comparison with Comparative Example 2. This seemsto be because, since Comparative Example 2 had small partition walldensity, strength was insufficient, and partition walls had a breakageduring the test by the internal pressure of the fluid. From this, thepartition wall density is more preferably 0.5 g/cm³ or more.

Comparison of Example 5 with Comparative Example 3

As shown in Table 1, Example 5 had no breakage of the main body duringthe production of the heat exchange element 1 in comparison withComparative Example 3. This seems to be because, though ComparisonExample 3 had high strength due to high partition wall density, it wasprone to break inversely, and thereby breakage was caused during theproduction of the heat exchange element 1. From this, in considerationof production of the heat exchange element 1, the partition wall densityis more preferably 5 g/cm³ or less.

INDUSTRIAL APPLICABILITY

The use of heat exchange element of the present invention is notparticularly limited in either the automobile field or the industrialfield as long as heat exchange is performed between a heated medium(high temperature side) and a medium to be heated (low temperatureside). In the case of using the heat exchange element for exhaust heatrecovery from exhaust gas in the automobile field, it can be used toimprove gas mileage of automobiles.

DESCRIPTION OF REFERENCE NUMERALS

1: heat exchange element, 2: end face (in the axial direction), 3:cells, 4: partition wall, 5: first fluid circulation portion, 6: secondfluid circulation portion, 7: outer peripheral wall, 8: bonding materiallayer, 10: heat exchanger, 11: heat exchange element-holding container,12: end face, 13: plugged portion, 14: inter-slit partition wall, 19:fluid sealing material

1. A ceramics heat exchanger comprising: first fluid circulationportions having a honeycomb structure having a plurality of cellsseparated by ceramic partition walls, extending through in an axialdirection from one end face to the other end face, and allowing a heatedmedium as a first fluid to flow therethrough, and second fluidcirculation portions being separated by ceramic partition walls,extending in the direction perpendicular to the axial direction, beingisolated from the first fluid circulation portions by the partitionwalls to be capable of heat conduction, allowing a second fluid to flowtherethrough, receiving the heat of the first fluid circulating in thefirst fluid circulation portions by means of the partition walls, andhaving cells for transferring heat to a medium to be heated as thesecond fluid; wherein the first fluid circulation portions and thesecond fluid circulation portions are alternately formed as a unit, thecells on the first fluid circulation portion side are smaller than thecells on the second fluid circulation portion side, and the partitionwalls have a density of 0.5 to 5 g/cm³ and a thermal conductivity of 10to 300 W/mK.
 2. The ceramics heat exchanger according to claim 1,wherein each of the second fluid circulation portions has a slitstructure having no separating partition wall or having 1 to 50separating partition walls.
 3. The ceramics heat exchanger according toclaim 1, wherein a plurality of the heat exchange elements are bondedtogether by means of a bonding material layer of heat resistant cement.4. The ceramics heat exchanger according to claim 1, wherein SiC iscontained in the ceramics constituting the partition walls.
 5. Theceramics heat exchanger according to claim 1, wherein the ceramicsconstituting the partition walls is Si-impregnated SiC.
 6. The ceramicheat exchanger according to claim 1, wherein the first fluid is gas, andthe second fluid is liquid.
 7. The ceramic heat exchanger according toclaim 1, wherein a catalyst is loaded on wall surfaces of the firstfluid circulation portions.
 8. A method for manufacturing a ceramicsheat exchanger comprising the steps of: forming a honeycomb structurehaving a plurality of cells separated by ceramic partition walls andextending through in an axial direction from one end face to the otherend face by extruding a ceramic forming raw material, forming slits withregard to a part of a plurality of cell lines to extend through thepartition walls forming the cells and the outer peripheral wall of thehoneycomb structure in the direction perpendicular to the axialdirection, and forming plugged portions plugged with a plugging memberon one end face and the other end face of the cells in the cell lineswhere slits are formed.